I know the topics about LED current sourcing and temp coefficient, but as my power source is limited at 3 amps, which also is the full load current of the LEDs, there is no risk of dead LEDS due to temp runaway. There are 10 LEDS in series and 10 of these chains in parallel.
http://www.ebay.com/itm/1pc-100Watt-High-Power-Bright-LED-Bulb-100W-Cool -White-Lamp-Light-led-beads-/140919675683?pt=LH_DefaultDomain_0&hash=ite m20cf779b23 One of these is operating for over 6 months now in a home luminary replacing a 300 Watt halogen tube (current sourced). http://www.lichtpuntnederland.nl/uplight-vloerlamp-met-leeslamp-brons.ht ml Most LEDS exhibit -5 mV /K or less (so 50 mV per 10), but also have 10 times its serial resistance The wiring resistance and a suitable (low) series resistor per LED may stabilize current run away. Just want to try how bad it is when regulating to say 33 Volts and measuring what is happening with the light and current. It may be possible that the temperature effect is simply not notable. Never draw conclusions on theory only ! Note that they need large heatsinks...as they need limitation of their temperature of around 60-70 degrees. http://www.ebay.com/itm/1-pc-up-to-100W-Watt-LED-Aluminium-Heatsink-Roun d-XXL-10W-20W-30W-45W-50W-100W-/160871698474?pt=LH_DefaultDomain_0&hash= item2574b3502a Gert -----Oorspronkelijk bericht----- Van: [email protected] [mailto:[email protected]] Namens John Woodgate Verzonden: vrijdag 1 maart 2013 17:37 Aan: [email protected] Onderwerp: Re: LED Chamber Lighting - drivers outside the chamber In message <of55b18620.c618ea44-on88257b21.00585dd6-88257b21.0059d...@selinc.com>, dated Fri, 1 Mar 2013, [email protected] writes: >John is right. You want to feed LEDs a constant current, and let them >drop whatever voltage they need. If I am not mistaken, LEDs have a >negative voltage temperature coefficient. With this being the case, >feeding a constant voltage will cause the current to increase as the >diodes warm up. The additional current will cause more heating. This >can lead to a "runaway" situation. I should have mentioned 'bad experience'. The runaway occurred only after everything appeared stable and was very sudden - too sudden to allow switch-off. Dead LEDs for sale cheap on ebay!!!! -- OOO - Own Opinions Only. See www.jmwa.demon.co.uk SHOCK HORROR! Dinosaur-like DNA found in chicken and turkey meals John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
